The invention relates to a method for oxidizing a pulverous fuel for a furnace, advantageously a flash smelting furnace, by means of a burner, in which case the oxidation takes place mainly owing to an effective mixing of two different combustion gases, the pulverous fuel and a possible extra fuel in the furnace space. The combustion gases are conducted into the furnace space in separate flows, so that oxygen is supplied centrally in an at least partly turbulent state, and air is fed in around it in several separate flows. The invention also relates to a burner for mixing pulverous fuel and combustion gas and for burning them in the said furnace space.
In the prior art there are known several ways for oxidizing pulverous fuel both with air, oxygen-enriched air and pure oxygen.
In the U.S. Pat. No. 4,210,315, a powdery substance is distributed as an annular, downwardly directed powder flow, which on a specially shaped surface disposed within the annular flow is directed and at the same time symmetrically distributed sideways by utilizing the dispersion air jets discharged from underneath the shaped surface. From around this suspension flow, still in a mainly annular flow, the combustion gas is conducted to be mixed into and to react with the powdery substance.
A typical requirement for combustion taking place in a cylindrical vertical shaft is that the powder-combustion gas jet must be parallel to the shaft and symmetrical with respect thereto, and this is realized for instance in the U.S. Pat. No. 4,392,885. There a mainly horizontally proceeding combustion gas is divided into a smooth, annular flow and turned to encircle the said pulverous flow in parallel direction to the reaction shaft.
Sometimes, when the annular combustion gas flow becomes too "thin", it must be conducted in spray-like sub-flows to encircle the above said pulverous flow and to be mixed thereto, like in the U.S. Pat. No. 4,490,170. The separate combustion gas jets are advantageously made to rotate.
In all these, the combustion gas comes from around a uniform pulverous flow either as a uniform annular flow or as separate jets.
As a difference with respect to the preceding examples, in the U.S. Pat. No. 4,331,087 the uniformly annular pulverous flow is, however, made to encircle a powerfully rotating combustion gas jet.
In the U.S. Pat. No. 5,133,801, a small amount of the oxygen is conducted in the center of the distribution member described in the U.S. Pat. No. 4,210,315 to supply extra oxygen from inside the pulverous flow.
In many cases, for instance while burning carbon, the pulverous fuel and combustion gas are mixed already before the reaction space, even before the burner proper. However, this does not always succeed, particularly if the employed combustion gas is pure oxygen and the fuel is some easily reacting pulverous substance. Wearing of the equipment also causes difficulties in this case.
In the present invention the drawbacks of the above-mentioned patents are overcome, and consequently the idea is realized in practice, too.